(a) Field of the Invention
The present invention relates to a multimedia communication system based on session initiation protocol (SIP). More specifically, the present invention relates to an SIP-based multimedia communication system for effectively providing mobility using a lifelong number and a mobility providing method.
(b) Description of the Related Art
The development of wired and wireless communication networks and people's desires for communications that can be used at any time and place are making a service environment where various communication networks coexist in an arbitrary place. A user can use different service networks depending on circumstances including the place where the user wants to carry out communication, the user's moving speed, the kind of information the user wants to use, communication performance the user desires, communication cost, and so on. Furthermore, terminals used for communication have various forms, and the choice of a terminal may affect the choice of a communication network.
The communication service user wants to use available communication service using various kinds of devices irrespective of place. For instance, the user may want to continuously watch VOD (Video On Demand) he/she has been watching in the living room, kitchen, or other rooms using a device placed in one of the rooms. For this, the SIP-based multimedia service provides consistent services to the user when the user wants to use an SIP uniform resource identifier of the user irrespective of the user's physical position and terminal. Mobility provided by an SIP-based multimedia communication system includes personal mobility, service mobility, session mobility, and terminal mobility.
In the meantime, SIP WG and SIP Proposal investigation (SIPPING) WG of IETF (Internet Engineering Task Force), an Internet protocol standardization organization, are carrying out standardization for providing personal mobility using SIP forking, service mobility according to a method of maintaining call control commands system-independently by registering a terminal capability or preference in an SIP register or using a call processing language (CPL), session mobility using third party call control or SIP REFER message, and terminal mobility using an SIP Re-INVITE message.
FIG. 1 shows a conventional personal mobility providing method in an SIP network service domain. Referring to FIG. 1, a communication peer who wants to make a multimedia communication with Alice requests a call setup targeting the SIP identifier of Alice. Here, it is assumed that Alice has alice@adsl.home.net 11 and alice@wlan.home.net 12 as her SIP identifier.
When the communication peer requests call setup targeting the SIP identifier alice@adsl.home.net 11, an SIP network server 13 of the adsl.home.net domain transmits a call to a physical SIP user agent currently registered as alice@adsl.home.net 11 through forking. Since there are two physical SIP user agents, tel:82421238282 15 and alice@host.home2.net 17, which are currently registered as alice@adsl.home.net 11, the call can be transmitted to these two SIP user agents 15 and 17.
When the communication peer requests call setup targeting the SIP identifier alice@wlan.home.net 12, an SIP network server 14 of wlan.home.net domain transmits the call to a physical SIP user agents registered as alice@wlan.home.net 12 through forking. Since there are three SIP user agents currently registered as alice@wlan.home.net 12, tel:82421238282 15, alice@laptop.home1.net 16 and tel:82161231004 18, the call can be transmitted to these three SIP user agents 15, 16 and 18.
In this manner, when a user attempts to set up a call targeting a peer's SIP identifier, the call is transmitted to a physical SIP user agent where the peer is currently located through the forking function of the SIP network server irrespective of the terminal at which the user is located. Accordingly, personal mobility in the SIP network using the forking function is provided.
In the meantime, a service profile is managed independently of terminals, and the SIP service is provided to the user based on the profile when the user uses the SIP service such that the user can be provided with the same service irrespective of the terminal at which the user is located. The service profile can include speed dials, a buddy list, media priorities, bell sounds, voice mail setup, and so on. Furthermore, call control commands are managed independently of terminals using a call processing language so that call control can be carried out in an integrated manner. In doing so, service mobility in the SIP network is provided.
Moreover, a user can continue a session in operation while changing a terminal, or another user can continue the session. Session mobility in the SIP network can be provided by using the third party call control or an SIP REFER message.
FIG. 2 shows a conventional session mobility providing method using an SIP REFER message. Referring to FIG. 2, when Alice 21 and Bob1 22 are carrying out multimedia communication between them, Bob1 22 moves a session to Bob2 23. Bob1 22 transmits the SIP REFER message 24 to Bob2 23 to request Bob2 to start a new call with Alice 21. Bob2 23 who has received the SIP REFER message 24 transmits an SIP INVITE message 25 to Alice 21 to request a new call setup. The SIP INVITE message 25 includes a request that makes Alice 21 complete the previous call set up between Alice 21 and Bob1 22 when the new call setup is accomplished.
When the new call setup between Alice 21 and Bob2 23 is accomplished, Alice 21 transmits an SIP BYE message 26 to Bob1 22 to finish the previous call set up between Alice 21 and Bob1 22.
In this manner, a user can continue a session in progress while changing a terminal, or another user can continue the session. Accordingly, session mobility in the SIP network can be provided.
Furthermore, it is possible to maintain a session and continue communication even if a terminal the user is currently using is moved between IP subnets. When the terminal is moved, the SIP informs the registrar of the terminal of a new IP address using the SIP REGISTER message. When the session is in operation, the SIP can inform a communication peer that the IP address has been changed using the SIP Re-INVITE message. In this manner, terminal mobility in the SIP network is provided.
FIG. 3 shows a conventional terminal mobility providing method using the SIP Re-INVITE message. Referring to FIG. 3, when Bob 32 is located in a home network, he transmits the SIP INVITE message 34 to Alice 31 to set up a multimedia call between Bob 32 and Alice 31. Here, it may happen that Bob 32, located in the home network, moves to a foreign network 35. Bob 33 who has moved to the foreign network can transmit the SIP Re-INVITE message 36 to Alice 31 to inform her that his IP address has been changed and continue a session.
While the above-described conventional techniques sufficiently consider mobility based on a logical SIP identifier allocated to a user, they barely consider user-centered mobility. The user is provided with services of various SIP network service providers. Accordingly, mobility cannot be provided due to the aforementioned problem when there are various different SIP network service providers.
In the case that an ADSL network operator and a WLAN network operator respectively provide SIP network services, for example, SIP identifiers provided by these two operators become logical identifiers independent of each other, as shown in FIG. 1.
In the case of personal mobility, a user is provided with personal mobility respectively for the two SIP identifiers so that a communication peer should distinguish the two SIP identifiers from each other. Furthermore, even when the forking function of the SIP network server is used, a call to all physical positions of a single user may not be set up.
In the case of service mobility, since a user is provided with service mobility respectively for the two SIP identifiers, different services may be provided to the user when the user moves between SIP network services.
There is no serious problem with session mobility because it is independent of logical SIP identifiers. However, there is a restriction on the session mobility that a terminal that attempts to move a session must be ready for receiving SIP messages all the time. Practically, a user is moved and then executes SIP service registration so that the session mobility cannot be provided.
Terminal mobility is not problematical because it is independent of the logical SIP identifiers. However, most terminals do not support multi-homing so that media packets of a session in operation may be lost while IPs are changed with each other. Furthermore, a communication peer should be informed of a terminal change.